How to tell someone I dont want.......?

To date them.? I have this friend of mine and he has asked me out about 20 times this summer (not even a month!) Hes asked me to the movies, his house, park, mall, and to Kohl's (he knows its my favorite store!).. And he also asks me why I wont date him and I try to be nice so I say "Because I like someone else at the moment" or he asks what are his chances with being with me which I say "Not likely I like someone else" and he then asked me to describe my perfect guy of which I said "Green eyes, black/dark brown hair, surfer body, smart, nice, funny, outgoing, and also romantic (bonus if hot)" and he then described the perfect girl for him which he said "You."... Yet the thing is he wont stop asking me out or asking me something related to us dating... He also once said to me "I guess Im just your gay bf until you get a real one" and then he said bf= best friend which I think he meant boy friend. He also has told his friends about me, and he calls me beautiful, nice, sweet, perfect and all these nice things but he doesn't get it I LIKE SOMEONE ELSE AND DON'T WANT TO DATE HIM! How do I tell hi nicely to stop asking me out and that he wont ever have a chance with me...